Control means

ABSTRACT

509,905. Automatic control systems; thermal switches. METALS &amp; CONTROLS CORPORATION. Jan. 24, 1938, No. 2327. Convention date, Jan. 26, 1937. [Class 38 (iv)] [Also in Group XXXVII] Temperature.-A heating system, using a furnace automatically stoked under the control of a room thermostat, includes an additional control, for the purpose of maintaining some fire at all times, which regulates the intermittent operation of the stoker when the room thermostat does not demand heat in such a way that the first period of rest after an operation of the stoker under room thermostat control is of a length dependent on the period of that operation. Connected in parallel with the room thermostat is a thermal switch which is heated electrically during operation of the stoker motor, the time taken by the switch to cool to a closed condition thus depending on the period of heating. The circuit arrangement is shown in Fig. 10. Supply mains 171, room thermostat 173 and stoker motor 169 are connected to terminals on the control device. This comprises a thermal switch of the snapaction-disc type which at an adjustable low temperature actuates two insulated contacts 29, 30 bridging separate pairs of switch contacts 35, 37 and 45, 47. The latter contacts are in parallel with the room thermostat and the former in a series circuit comprising a resistance 109, and a second thermal switch consisting of a bimetallic element 53 and a light spring element 55. Resistances 131, 133 in series are in parallel with the stoker motor. The second thermal switch is closed at an adjustable low temperature to short circuit the resistance 133. The resistances heat the thermal switches. When the room thermostat is not calling for heat the stoker motor is switched on through contact 30, and resistance 109 (through contacts 53 and 29) and resistance 131 heat up the switches at a maximum rate. The thermal switch contacts 29, 30 consequently open at a definite temperature (which is not adjustable), and to adjust the &#34; on &#34; period to suit the furnace conditions the opening temperature of the second thermal switch 53, 55 is made variable; when this switch opens the resistance 133 is put in series with resistances 131 and 109, thus prolonging the time taken for the contacts 29, 30 to open the resistance circuit and stop the motor. The &#34; off &#34; period which now begins lasts until the switch 29, 30 has cooled sufficiently to close, and is variable, by an adjustment provided for this switch, to suit the furnace conditions. When the room thermostat calls for heat it will energise the stoker motor and heat resistance 131, thus raising the temperature of the thermal switches. The time taken for the switch 29, 30 to cool again to the temperature required to start the fire-maintaining action of the stoker motor will thus depend upon the period of stoker operation under room thermostat control. The construction of the thermal switches is shown in Figs. 5 and 9. They are mounted in a casing 17 the rear of which is closed by the heating resistances, wound on mica plates and sandwiched between insulated steel plates. The contacts 29, 30 are carried by a disc 27 guided by studs 31 fixed in a bracket carrying notched pillars 21 retaining in position a composite dished thermal element 23 connected by a shaft 25 to the disc 27. The temperature at which the disc 23 will snap the contacts 29, 30 into closed position is determined by a screw 65 which is adjustable in a screwed bush 63 by means of a sealed knob 67 co-operating with an index on a mounting plate 1 which carries the casing 17. The fixed contacts of the switch are secured to terminals fixed in the sides of the casing. The bimetallic element 53 of the second thermal switch and the spring 55 are secured respectively to the switch contacts to which they are connected and carry mating contacts 57, 59. A porcelain member 89 carried by a spring element 87 loosely secured to a bracket 83 may be adjusted to determine the opening temperature of the switch by a screw 75 bearing on the member 87 and similarly arranged to the screw 65.

June 22,v 1943.

V. G. VAUGHAN ETAL',

con'rRoL MEANS Original Filed Jan. 26, 1937 4 Shee'ts-Sheet 1 FIGA.

June 22, 1943.

` V. G. VAUGHAN ET AL CONTROL MEANS Original Filed Jan. 26. 1937 4 Sheets-Sneek 2 June 22, 1943.

CONTROL MEANS v. G. vAuGHAN E'rmL Original Filed Jan. 26, 1957 4 Sheets-Sheet 3 June 22, 1943.

FIG,I4. @La 'W W W v. G. vAuGHAN-ErAL coNTRoL lmms original Fed Jan. 26. 19s? y MG16.

4 Sheets-Sheet 4 Patented June 22, 1

UNITED STATE CONTROL MEANS Victor G. Vaughan and John D.

ss.,4 assigner: to Metals boro, Ma

Controla Corporation, Attleboro. Mass.. a corporation of husetts Original application January 28.1937. Divided and this application April 16,

1941, Serial No. 388,826

7 Claims.

This invention relates to a method of and sys- 'tem for regulating heating, and with regard to certain more specific features, to a method of and system for regulating the heating of enclosed spaces, such as houses, and control means therefor.

This application is a division of our copending application Serial No. 122,372, nled January 26, 1937, Patent No. 2,254,054, Aug. 26, 1941.

Among the several objects of the invention may be noted the provision of a method of and system for heating of the class described, which is particularly adapted for use in connection with a coal-fired furnace unit, and which is adapted. when so used, to control an automatic stoker for said furnace unit in such manner as to successfully maintain a suillcient fire in the furnace at all times, so that upon demand for heat, the furnace is capable of supplying heat without a considerable interval of time elapsing, but which, at the same time, is so correlated with the room thermostat or other primary control for the furnace, that the production of excessive heat at unwanted times, only in order to maintain a fire in the furnace, is avoided; and the provision of a novel form of control means for use in connection with a method and system of the class indicated, said control means being rugged and reliable in its operations. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, steps and sequence of steps, features of construction, and arrangements of parts, which will be exemplified in the structures and methods hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated one of various possible embodiments of the invention,

Fig. l is a front elevation of a control employed in the present invention;

-Fig. 2 is a bottom plan view of the control of Fig. 1:

Fig. 3 is an end elevation of the control of Fig. l;

Fig. 4y is a hack elevation of the control of Fig. 1;

Fig. 5 is a horizontal cross section, taken substantially along line 5 5 of Fig. 1,'

Figures 6, 7, 8 and 9, are vertical cross sections taken lsubstantially along lines 6 6, 1 1, I U, and 9 9, of Fig. 5;

Fig. 10 is a diagram illustrating the electrical connections of the control of Fig. l;

Figures 11 and 12 are graphs indicating certain time-temperature relationships hereinafter to be described;

Fig. 13 is an enlarged cross section of a fragment of Fig. 5; and,

. over-al1 eillciency of Serial No.

Figures 14. 15 and 16 are diagrams illustrating certain on and off periods provided by the control system of the present invention.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

The present invention relates to a combustion control means, with particular regard to apparatus of a type known as a "stoker timer or hold nre" control.

This form of control is commonly employed in governing the operation of coal burners and the like, where the fuel is mechanically fed from a source of supply to a combustion pot, and air is provided under forced draft in the proper amounts to support efficient combustion in the pot at a rate proportional to the fuel feed. In governing the operation of burners of this type. it is also usual to employ other control means such as, for example, room thermostats, combustion switches, and boiler temperature or pressure limiting devices. For instance, when the mechanical burner is employed to heat a building, socalled room thermostats respond to temperature changes in the living quarters and start or stop the burner in accordance with the degree of heating,desired.

Combustion switches operate to shut the burner down if the flame should extinguish, thus preventing a continuing supply of unburned fuel in the combustion pot. K

Limit controls act to hold the heating plant temperature or pressure within minimum and maximum preselected values.

Between periods of demand of auxiliary controls such as room thermostats and limit controls, it is common practice to discontinue the supply of fuel and air to the burner, to conserve fuel, prevent over-heating of the living quarters, and prolong the life of the burner mechanism. Yet it is necessary during such periods to maintain ignition of the fuel in some degree, so that upon renewal of demand normal combustion will be assured.

Various methods of accomplishing this have heretofore been employed, and will be brieily outlined, in order more fully to understand the present invention.

One prior method is to slow down the operation of the fuel feeding mechanism to the point where a minimum amount of fuel and air s-fed to the combustion pot. This method has the disadvantages of complicating the plant by adding speed changing mechanisms and reducing the combustion by burning fuel at more than one rate of feed.

A second prior method is to operate the burner from a low limit control subjected to heating plant temperatures, the low limit control coming into playduring an "off period when the heating plant cools down to a predeterlnined point. This method is not entirely dependable, because it is possible for the heating plant. to deiay so long in cooling, under certain conditions, that the fuel in the combustion pot will have burned itself out before mechanical feed is reestablished.

A third prior method is to cause the burner to start up and run for brief intervals at certain regular intel vals during its olf period. In this way, the brief on" or sustaining intervals need not be long enough to continue heating, but merely of sufficient duration to replace the exhausted fuel in the combustion pot with a fresh charge well ignited. Similarly, regardless of heating plant temperature or any other resultant temperature factor, this action can be initiated at intervals related to the length of time an idle fire can be held over in the combustion pot, which is the most satisfactory relation on which to base hold fire control.

Until the present invention, however, there have been objections to even this type of control, principally because of the limitations of the clockdriven timing apparatus employed. Unrelated as such clock-driven apparatus is to other temperature-determining factors, it can cause the burner to come on at times when it is not needed, for example, at the end of a room thermostat demand period, when continued burner operation means overheating. Moreover, such clock-driven timing devices are, as a rule, relatively costly and delicate, and complicated as to timing adjustments. f

The present invention overcomes these objections to a large degree, providing a control device which is simple, rugged and relatively low in cost, and making possible a system of adjustable control wherein the elements have a reciprocal in iiuence on each other, so that their joint action accomplishes the result desired.

Referring now more particularly to the drawings, numeral i indicates a panel upon which the control device of the present invention is mounted. The panel carries, along one edge thereof, electrical terminals or binding posts 3, 5, 1, 9, Il, and I3, the significance of which will hereinafter be explained. Mounted on the rear side of the panel I by means of pillars I5, is a rectangular box or casing I1, which houses the elements of the control proper. Inside the box I1 there is provided a suitably mounted shelf or bracket I9.

Extending from the bracket I9 in the direction of the open side of box I1 (e. g., away from the panel I), are a plurality (four in the present embodiment) of slotted pillars or posts 2 I The slots of the posts 2| receive the periphery of a snap-act ing dished thermostatic disc 23, which may, for example, be of the type shown and described in John A. Spencer Patent 1,448,240, dated March 13, 1923. A characteristic of the snap-acting thermostatic disc 23 is its tendency to reverse its curvature, from concave to convex, or vice versa, with a snap-action, in response to changes of ambient temperature. The peripheral mounting of the disc 23 in the post 2| leaves the central portion of the disc 23 free to undergo such snapping movement, in response to temperature changes.

Secured to the central region of the thermostatic disc 23 in such manner as to be movable therewith, is a sliding shaft 25, which extends through the shelf I9. On the other side of the shelf I9, the shaft 25 mounts a switch plate or disc 21, which in turn serves to mount diametrically oppositely disposed contact buttns 9 1 members 29 and 39. The contacts -29 and 3U are insulated from the disc 21 with a suitable dielectric material such as mica. Posts 3|, mounted on the shelf I9, extend through suitable openings 33 in the disc 21, in order to prevent rotation of said disc 21 relative to the shelf I9. Numerals 35 and 3" indicate a pair of contact plates that are positioned on the shelf I9 in such location that they are engageable by the movable contact 29 on the disc 21. Suitable insulating material 39, such as mica, insulates the contacts 35 and 31 from the shelf I9. The contacts 35 and 31 are respectively supported by terminal pieces 4I and I3, which are mounted on the side and end walls, respectively, of the box I1, b"t are electrically insulated therefrom.

Similarly positioned on shelf I9 to cooperate with the movable contact 30 on the disc 21 are stationary contact plates 45 and l1, which are supported on terminal pieces 49 and 5I, respectively, mounted ln the opposite side wall of the box I1. The stationary contact plates 35, 31, 45 and 41 are, preferably, riveted in position on the shelf I9, but in a manner such that they are electrically insulated therefrom. However, the rivets for contact plates 35 and 45 extend through to the opposite side of shelf I9, where the rivet of contact plate 35 serves to support the end of a composite thermostatic metal blade 53, and the rivet of contact plate 45 similarly supports the end of a spring or resilient blade 55. The blades 53 and 55 are so mounted that their free ends overlie one another, the blade 53 being provided with a contact button 51 cooperating 'with a similarI contact button 59 on the blade 55. The blade 53 is thus electrically connected to the contact plate 35, while the blade 55 is connected to the contact plate 45. The blades 53 and 55 are electrically insulated from the shelf I9, as by strips of mica or the like 6I.

Numeral 63 indicates a threaded bushing that is mounted in the bottom of box I1 in position coaxially with the shaft 25. The bushing 93 receives the threaded end of a shaft 65 that extends forwardly through the panel I. In front of the panel I the shaft 65 mounts a knob and dial assembly B1, the periphery oi the dial containing suitable indicia as indicated in Fig. l. An index pointer 69 (Fig. 1) is provided for the purpose of reading the indicia on the dial 31..

The dial 51 is preferably provided with a peripheral projection or stop 1I, that abuts the pointer B9 when the dial 61 is rotated in a counterclockwise manner, to zero position.

The inner end of shaft 65, within the box I1, constitutes an abutment limiting the downward travel of the shaft 25. By the limitation of the downward travel of the shaft 25, the extent of reversedshlng of the thermostatic disc 23 ls controlled, and this control of the extent of dishing-constitutes a control of the temperature at which the thermostatlc disc 23 will snap upwardly. That is to say, if the disc 23 were permitted, by removal of the abutment provided by shaft 55 for shaft 25, to snap, upon reaching a predetermined high temperature, to its unrestrained, maximum extent of concavity Yhot position, then, due to the inherent operating differential of the disc, it would not snap back to opposite concavity (cold position) upon cooling until a certain minimum low temperature was reached. But by restraining the extent or amount of concavity the disc assumes in its "hot position, the temperature in a cooling A second threaded bushing 1a le likewise mounted in the bottom of box |1, in position substantially on a line with the contact buttons 51 and 59 on the blades 53 and 55. respectively. The bushing 13 receives the threaded end of a shaft 15, which likewise projects forwardly through the panel I and mounts a knob and dial assembly 11 similar to the knob and dial assembly 51. The dial 11 is likewise provided with indicia and a pointer 19 and stop 9|, similar to the pointer 59 and stop 1| for the dial 91.

Inside the box I1, angle bracket 03 is riveted near the bushing 13. A wire clipl 95 loosely secures the bight of a U-shaped spring 31 to the bracket 33. The inner end of shaft 15 abuts one end of the spring 31, while the opposite end of the spring 91 supports an insulating button 39 (which may be made, for example, of porcelain),

which button 39 underlies the contact button 59 on blade 55. By threading the shaft 15 into the bushing 13 the button 09 is pushed against the button 59, and since the spring 01 is considerably stiller than the blade 55, the resultant effect is to change the position of the' contact button 59. Since the bimetallic blade 53 curls freely under changes of ambient temperature, it will be seen that this adjustment of the position of button 59 constitutes an adjustment for the temperature at which contact buttons 59 and 51 will come together to complete a circuit. However, the spring 91 is not so stifl' that ,it is incapable of yielding under pressure of the bimetallic blade 53, and thus no fixed abutment is presented.

The edges of the end walls oi' box I1 are turned outwardly to form flanges 9| and 93, respectively, which flanges 9| and 93 mount double binding post elements 95 and 91, respectively. The function of these binding posts 95 and 91 will be explained hereinafter.

The edges of the side walls of the box I1 are turned outwardly to form flanges 99, which serve to mount a composite laminated heating unit |0| next to be described. Referring to Fig. 13, the lowermost layer or lamina of the heating unit |0| comprises a rectangular metallic (steel, for example) plate I03. surmounting the plate |03 is a similarly shaped rectangle of heat-resistant, electrically insulating material |05, such as mica. surmounting A the mica sheet |05 is a mica sheet |01, somewhat smaller in size, upon which is wrapped, fiatwise, a low-resistance heating coil |09. The shape of the coil |09 is indicated in Fig. 6. The ends and ||3 of the coil |09 extend out from the ends of the heating unit 0|, for electrical connections hereinafter to be described.

surmounting the mica sheet |91 is a plain mica sheet 5, and surmounting this sheet ||5 is a metallic plate ||1 like the plate |03. surmounting the metallic plate I1 is a mica sheet ||9, and surmounting this mica sheet ||9 is a mica sheet |2| upon which is wrapped a relatively high resistance electrical heating coil |23 (see Fig. 7).

The ends |25 and |21 of the coil |23 extend from the ends of the heating unit |0| and a middle tap or connecting wire |29 extends from the side of the heating unit |0|. The middle tap |29 divides the heating coil |23 electrically into separate, series-connected coils |3| and |33, both of which together make up the coil |23.

Sur-mounting the mica sheet |2| on which the coil |23 is wrapped is a mica sheet |35, and the uppermost lamina of the another metallic plate |31, similar\to the plates |03 and 'I'he various laminae of the heating unit |3| are secured together and to the flanges 99 by means of screws |39 and nuts |4l. The mica sheets |01 and I2i, which carry the windings |09 and |23, are provided with suitable notches |43 along their edges in the region occupied by the screws |39, so there is no danger of the respective winding shorting to the screws |39.

The electrical connections for the control just described will now be set forth. For simplicity, the electrical connections are eliminated from mt of the figures loi' the drawings, butl they are shown in diagrammatic form in Fig, 10, to which attention is now directed.

Binding post 3 is connected by a wire |45 to terminal piece 5I, which is in ,turn connected to contact plate 41. 1 Another wire |41 connects binding post 3 to binding post 1. Binding post 5 is connected by a wire |49 to one side of double binding post 91, by a wire |5| to terminal piece 49, and by a wire |53 to binding post |3. Binding post 9 is connected by a wire |55 to binding post l l, and by a wire |51 to one-half of double binding post 95.

One end of heating coil |09 is connected to the other side of double binding post by a wire |59, while the other end ||3 of heating coil |09 is connected to terminal piece 43 by a wire |9|. One end |25 of heating coil |23 is connected by a wire |53 to double binding post 95. 'I'heother end |21 of heating coil |23 is connected by a wire |05 to double binding post 91. The central tap |29 of heating coil |23 is connected by a wire |31 to terminal piece 4|. 1

'I'he system in which the control thus described is used thus comprises an 4automatic electric stoker mechanism of any desired type, which preferably has a motor or other electrically powered or controlled drive |99. Binding posts and |3 are connected to the stoker motor |59 or power control circuit. Binding posts 1 and 9 are connected to power lines |1|, such as a l10- volt A. C. line. Binding posts 3 and 5 are connected to a room thermostat |13, positioned in vthe space to be heated,or to some other similar auxiliary control system (which may include the customary boiler limit controls and the like).

In operation, the thermostatic disc 2'3 is arranged so that, upon rise of temperature, it moves from an upwardly conical position to a downwardly conical position (with respect to Fig. 5), or, in other words, breaks the connection between contact buttons` 29 and 30 and their respective contact plates 35 and 31, and 45 and 41, respectively, upon rise in temperature. Upon dropping temperature, the reverse action is rue.

Similarly, the bimetallic blade 53 is so arranged that upon rise of temperature it separates its contact 51 from the contact 59 on resilient blade 55, while upon a drop of temperature, the blade 53 so moves that the contacts 51 and 59 are brought into juxtaposition. The changes in ambient temperature which bring heating unit comprisesl about the movements of thermostats 23 and 53 are brought about by the heating eiiect or absence of it from the heating coils |09, |3|, and |33.

The operation of the device as thus described is as follows:

Assume that the room thermostat |13 is satisfied (room thermostat contacts open) and the present control device has been cooling and is about ready to start a hold fire run. 'Ihermostat 53 characteristically closes contacts 51 and 59 rst as the temperature of the device falls, but, the room thermostat circuit being open, and thermostat 23 not yet being cool enough to close, nothing results. A check of the wiring will show that while binding post 9 is connected to thermostat 53 through heater |3| and terminal piece 4|, terminal 49 represents a dead end, so there is no flow of current through any part of the device as yet.

In due time, however, disc thermostat 23 cools suillciently and snaps to its closed position. When this takes place, the circuit through terminal pieces 4| and 43 is closed by bridging contact 29, and the circuit through terminal pieces 40 and 5| is closed through bridging contact 30. Now tracing from binding post 9, it will be noted that binding post Il is energized, and tracing from binding post 1, it will be seen that binding post |3 is energized through terminal piece 5|, bridging contact 30, and terminal piece 49. Thus the stoker motor |59,is lstarted. Again tracing from binding post 9, it will be seen that heaters |09 and |3I are energized, the former by way oi' terminal piece 43, bridging contact 29, terminal piece 4|, bimetallic blade 53, spring blade 55, terminal piece 49, bridging contact 30, terminal piece 5|, and binding post 1, andthe latter by way of tap |29, wire |51, terminal piece 4|, bi-

metallic blade 53, spring blade 55, terminal piece 49, bridging contact 30, terminal piece 5|, and binding post 1. Actually heaters |09 and |3| are in parallel connection to terminal piece 4|, and heater |33 is shorted out between terminal pieces 4| and 49. V

The result of this is that heating coils |09 and '|3| raise the temperature within the device,

eventually causing thermostats 53 and 23 to break their associated circuits. Thermostat 53 ordinarily breaks rlrst and heater |33 is thus placed in series with the parallel-connected heaters |09 and |3|, continuing the heating of thermostat 23. When this latter thermostat 23 breaks its connections, the stoker motor |59 is shut of! and the several heaters |09, |3|, and |33 are deenergized.

The cycle just described is what is called the ,"on" period, or period o! energization of the controlled device, and is ordinarily of from, say, two

to ten minutes duration depending upon the y hold fire characteristics of the particular stoker unit involved. The cycle following the "on period is called the oil period, or period of deenergization of the controlled device, and may vary from, say, thirty minutes to an hour and a half, depending also upon the hold ilre characteristics of the stoker unit.

Variations in length oi' "on" time' settings, in view of variable settings for "oiP time, are accomplished in the following manner. The thermostat 23 is the governor of "ofP time, its snapping-oi! point (on a temperature rise) being fixed, and the adjusting mechanism (shaft 55, dial 51, etc.) associated with it controlling its snapping-on point, or in eiiect, its temperature differential. By lowering the snapping-on point. or, in other words, widening the diierential, the cooling or oil period is prolonged. Conversely, by raising the snapping-on point, or, in other words, narrowing the differential, the cooling or ofi period is decreased. This effect may be visualized graphically by reference to Fig, il, which is a graph in which the abscissae and ordinates represent time and temperature, respectively. u Line A represents the (iixed) snappingofi temperature of thermostat 23. Line B is the temperature curve of the interior of box l1, which is equivalent to the temperature of thermostat 29. At the abscissal origin, point C, the thermostate 23 is assumed Just to have snapped oif," hence the curve B shows a cooling phase. which means that the thermostat 23 will cool. The cooling phase continues until the thermostat 23 reaches its snapping-on temperature which is adjustable by manipulation of the dial 91. Several points C1, Cn, Cs. C4, Cs, and Cs are shown as exemplary of various settings of snapping-on temperatures. When the selected snapping-on point (C1, Cz. Ca, C4, Cs, or Cs) is reached, thermostat 23 snaps on and curve B enters a heating phase, with heaters |09 and I3I operating in parallel. For clarity, curve B is shown as a family of dotted lines B1, Bz, B3, B4, B5, and Bs, arising respectively from points C1. 2,03, C4, C5, and Cs. 'Ihe oiT' period of time is represented by the abscissal distance of point C from the selected one of points Ci, Cz, Ca, C4. C5, and Cs, and is indicated in Fig. 11 by the dimension lines T1, Tn, Ts, T4, Ts, and Ts respectively. Since the snapping-oil' temperature of thermostat 23 (line A) is held constant it makes no difference how long it takes to reach this temperature, as thermostat 23 always starts its cooling cycle from the same temperature level. As already described, the cooling or oft period following thereafter is varied by shifting the snapping-on temperature or differential.

Consider, next, the variation in setting of on" period of the control device. This is governed by the setting of thermostat 53, which, it will be seen from the diagram, controls the operation of heater |33. The setting of thermostat 53 is accomplished by manipulation of shaft 15. dial 11, etc. When thermostat 53 is closed, heater |33 is shunted out, and when thermostat 53 is open, heater |33 is in series connection with heater |3|, which latter heater may be at the same time in parallel connection with heater |59. When heater |3| and heater |09 form a parallel connection, a relatively fast heating rate results, aiiecting both thermostats 53 and 23. However, when thermostat 53 opens, heater |33 Joins the parallel system in a series relation and the rate o! heating originally started is considerably decreased, although this connection still results in a temperature rise, approaching the snapping-oil' point of thermostat 23.

For a diagrammatic representation of this effect, see Fig. 12. In Fig. 12 the ordinates again represent temperature, and the abscissae time. Line A has the same significance as i i Fig. ii. Line D is the temperature curve of the interior oi box I1, which is equivalent to the temperature of thermostats 23 and 53. The initial portion of line D represents a heating phase (heaters |09 and |3| operating in parallel), and may be considered as the duplicate of any one oi' the curves Bi, Bz, Ba, B4, Bs, or B4 of Fig. 1l. This heating phase continues until the temperature at which thermostat 53 opens is reached. This temperature, which is represented by points Ei. En, Ea, E4, E5, and Ee, is adjustable, by means of the settings of dial 11. When the selected temperature (El, Ea'Ea. E4, E5, or Ea) is reached,"

thermostat 53 opens its circuit and the arrangement of heaters is changed, heater |33 coming into series with parallel-connected heaters |09 and |3|, with a consequent decrease inrate of heating. For clarity, curve D is shown, in this new phase, as a family of dotted lines Di, Dz, Da, D4. Ds, and Ds, arising respectively from points E1, Ez, Es, E4, E5, and Ee. 'Ihls new heating phase lasts until the temperature reaches the snapping-01T temperature of thermostat 23. represented by line A. Depending upon the particular setting of thermostat 53 (and hence the curve D1, Da, Da, D4, D5, or De being followed), this value will be reached at respective points indicated as Fi, Fs, Fa, F4, F5, or Fs. The on period of time is occordingly represented by the abscissal distances between commencement of the rst heating phase (the origin in Fig. 12) and the points F1, Fn, Fs, F4, Fs, and Fs, which distances are respectively indicated in Fig. 12 by the dimension lines t1, tz, ta, t4, t5, and to.

Thus it can be seen that if the temperature at which thermostat 53 opens is raised, the time required to bring the net temperature to the snapping-oil point of thermostat 23 may be lessened, hence an adjustment of length of on period is achieved.

As has already been outlined, the length of "ofl period of the device is regulated by the length of cooling cycle of thermostat 23, which obviously will be unaffected by any cooling action of thermostat 53. Thus independently adjustable timing periods of on and off action are obtained. Since the eifect sought is one that is determinable in units of time in each instance, the calibration of dials 51 and 11 is preferably in time units.

To go back to the operation of the device in tor. At the same time the heaters |3| and |33, now in series, would be energized from binding post-9 to heater |3| to heater |33 to binding post 5, through auxiliary or room thermostat system |13 to binding post 3 to binding post 1. Since thermostats 53 and 23 are open, heater |33 is no longer shunted, and he'ater |09 is not energized. The purpose of continuing the energization of heaters |3| and |33 in series, is to keep thermostats 53 and 23 heated, and thus open. Therefore, as long as the auxiliary controls, such as the room thermostat |13, call for heat, the stoker motor |99 would continue to run, and thermostats 53 and 23 would be held open. Upon termination of the room thermostat |13 demand, the stoker motor circuit |63 would be broken through the room thermostat |13, and hence the stoker would shut down. It would not start up for a. hold re on period until thermostats 53 and 23 had cooled suillciently to close, or, in other words, the off period would commence at the time of the stoker shut-down, regardless of the relation of its previous hold ilre cycles to the length of the demand run just completed.

At this point an improvement in'stoker control means made possible by the present invention will be brought out. It is obvious that the length of the demand period of room thermostat |13 typical usage, it would be well at this point to I. Room thermostat |13 calls for heat during on period.

II. Room thermostat |13 calls for heat during oif" period.

I. 'Referring again to Fig. 10, ifthe circuit across binding posts 3 and 5 should close while the stoker motor |09 was running as during an on"'period, heaters |09 and |3| would remain energized, and |33 shunted, until thermostat 53 was sumciently heated and opened. When thermostat 53 opened, heater |33 would then bey in series with parallel-connected heaters |09 and |3|, as outlined before until thermostat 23 was sumciently heated and opened. Then, with both thermostats 53 and 23 opened, the circuit to the stoker motor would be traced as follows: One' side would be connected as shown from binding post 9 to binding post the other side from binding post 1 to binding post 3, through the room thermostat (or other auxiliary control system) to binding post 5, and thence to binding post I3, continuing energization of the stoker momay vary considerably from cycle to cycle, depending upon outdoor temperature. weather conditions, time of day, and so on. Now in the face of varying lengths of demand periods by room thermostat |13, if the stoker control means enters an o period of x'ed length immediately following the room thermostat demand cycle, as common mechanically operated stoker timers with cycle synchronizing means usually do, then when the room thermostat demand period is very short and the stoker fire does not have suflcient time to reach a vigorous state under its control, the off period of the timer, being fixed, may be too long, and the idlestoker ilre may burn out or burn so low that reestablishment of normal combustion in the stoker is hampered. Maintenance of uniform temperatures, in the living quarters may thus be considerably upset.

If, on the other hand. the first off period of the Stoker timer following cessation of a demand by the room thermostat is timed in relation to the length of the room thermostat demand period, then an improvement of stoker operation results. At the same time, the oil period of the stoker timer in question should be regulated more in the case of a short room thermostat demand period than in the case of a long one, tothe extent that in event of a protracted room thermostat demand period, the normal length of the oit cycle of the stoker control should preferably not be exceeded greatly.

In the present invention this type oi?v compensation is brought about by so proportioning the thermal constants of the stoker timer heating elements and thermostats that the desired resuits are obtained. Thus, when the room thermostat |13 is independently operating the stoker, heating of the thermostats 23 and 53 takes place, either with relative rapidity and then more slowly,.or at the slower rate only, as described, and, up to the degree of heating normally obtained in a regular stoker control on cycle, the amount of heat input to the thermostats 23 and 53 will depend on the length of the room thermostat demand period. Thus, the length of the first off period of the stoker timer following thereafter, or in other words, the length of the rst cooling period of thermostat Il and 53. depending on the degree of heating reached. will be in relation to the length of the room thermostat demand cycle asdesired.

The conditions just discussed are illustrated in Figures 14, 15, and 16. In these figures, horizontal distances represent time. Fig. 14 shows the theoretical on and oi! operations of an undisturbed stoker timer, the shaded areas X representing the periodical on" intervals. Fig. 15 shows an assumed set of room thermostat cycles, on periods (or periods of demand for heat) being diilerently shaded and indicated at YI, Y2, YS, Yl. Y5, YB, and Y1, respectively. Fig. 16 shows the cycle oi operations that take place when the stoker timer and the room thermostat of Figures 14 and 15, respectively, are combined in a single circuit, as provided by the present invention. From Fig. 16 it will readily be seen that a stoker timer otP' period always follows a room thermostat on" period, regardless of the elapsed time since the previous stoker timer off" period. It will further be seen that the length of the stoker timer "oiT period is roughly proportional to the length of the room thermostat on period, up to a certain maximum oiT period; for example, oiI" period Zi, which follows room thermostat on period Yi (a relatively short on period), is itself relatively short. Similarly, "oil" period Z3, which follows relatively long room thermostat on period Y3, is of substantially maximum length, and "oi" period Z5, which follows exceedingly short room thermostat on period YS, is oi' relatively shortest duration.

1I. Again referring to Fig. 10, 4if the circuit across binding posts 3 and 5 should close during an oi period oi' the hold fire device:

IIa. Thermostat 53 might be closed and thermostat 23 open. IIb. Both thermostats 53 and 33 might be open.

IIa. In this case, the stoker motor |59 would be started up by the closing oi' the room thermostat |13. Heater i3i would be energized and heater |33 shunted, thus heater i3l would raise the temperature of thermostat 53 quite rapidly (having less resistance than the combination oi heaters I3i and |33 in series) and in due time thermostat 53 would open. Upon so opening, the shunt would be removed from heater |33, which, now in series with heater lil, would continue heating ot both thermostats 53 and 23 at a moderated rate while the stoker motor circuit was held closed by the room thermostat |13 as under case I.

IIb. If the room thermostat |13 should close while both thermostats 53 and23 were open, the stoker motor |69 would start up immediately. Also, heaters I3I and |33 would be energized, in series, and would heat thermostats 53 and 23 moderately, and hold them open as, under I and IIa.

'Ihus it will be seen how the system and control of the present invention function in a manner which is highly desirable for Stoker hold-lire control, achieving al1 ot the objects and meeting all of the difnculties heretofore set forth in this specification.

Our co-pending application Serial No. 122,372, led January 26, 1937, contains claims to the stoker control per se.

In view ot the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Whatis claimed is:

1. In a heating system, a heating plant, an electrically controlled automatic stoker supplying fuel to said heating plant, and an electric circuit for the control of said stoker, said circuit including a room thermostat positioned in the space to be heated and an intermittent hold tire timer, said room thermostat being connected in such manner as to be capable of commencing the operation of said automatic stolcer when said thermostat demands heat, regardless of said hold rire timer, said hold fire timer comprising contacts connected in parallel with said room thermostat for controlling said stolzer circuit, a plurality of heating devices. switching means for controlling said heating devices, heat responsive means for intermittently actuating said contacts and said switching means to provide intermittent operation of said stolzer during periods of no heat demand and so controlling said heating devices as to provide first one rate of heating and then a different rate oi heating during a cycle of operation, and means controlled by said room thermostat whereby the operation of said stoker by said timer following a call for heat by said room thermostat is delayed for a period of time which varies in accordance with the duration of operation under control of said room thermostat.

2. In a heating system, a heating plant, an electrically controlled automatic stoker supplying iuel to said heating plant, and an electric circuit lor the control of said stoker, said circuit including a room thermostat positioned in the space to be heated and an intermittent hold fire timer, said room thermostat being connected in such manner as to be capable of commencing the operation ot said automatic stoker when said thermostat demands heat, regardless of said hold nre timer, said hold tire timer comprising contacts connected in parallel with said room thermostat for controlling said Stoker circuit, a plurality of heating devices, switching means for controlling said heating devices, heat responsive means for intermittently actuating said contacts and said switching means to provide intermittent operation o! said stoker during periods of no heat demand and so controlling said heating devices as to provide iirst one'rate of heating and then a diierent rate oi.' heating during a cycle of operation, and means controlled by said room thermostat whereby the first operation of said stoker by said timer iollowing a call for heat by said room thermostat is delayed for a period ot time which varies in accordance with the duration ot operation under control of said room thermostat.

3. In a heating system, a heating plant, an electrically controlled automatic stoker supplying fuel to said heating plant, and an electric circuit for the control oi' said stoker, said circuit including a thermostat positioned in the space to be heated and an intermittent hold fire timer, said thermostat being connected in such manner as to be capable oi.' commencing the operation oi said automatic stoker when said thermostat demands heat, regardless of said hold tire timer, said hold nre timer comprising contacts connected in parallel with said thermostat for controlling said stolser circuit, a plurality o! heating devices,

switching means for controlling said heating devices, heat responsive means for intermittently actuating said contacts and said switching means to provide intermittent operation of said stoker during periods of no heat demand and so controlling said heating devices as to provide first one rate of heating and then a different rate of heating during a cycle of operation, and means controlled by said thermostat whereby the operation of said stoker by said timer following a call for heat by said thermostat is delayed for a period of time which varies in accordance with the duration of operation under control of said thermostat.

4. In a heating system, a heating plant, an electrically controlled automatic stoker supplying fuel to said heating plant, and an electric circuit for.

the control of said stoker, said circuit including a first thermostat positioned in the space to be heated and an intermittent hold fire timer, said first thermostat being connected in such manner as to be capable of commencing the operation of said automatic stoker when said thermostat demands heat regardless of said hold re timer, said hold fire timer comprising contacts, connected in parallel with said first thermostat for controlling said stoker circuit, a plurality ,of heat-- ing devices, switching means for controlling said heating devices, a second thermostat for intermittently actuating said contacts and said switching means to provide intermittent operation of said stoker during periods of no heat demand and so controlling said heating devices as to provide iirst one rate of heating and then a different rate of heating during a cycle of operation, and means controlled by said first thermostat whereby the operation of said stoker by said timer following a call for heat by said first thermostat is delayed for a period of time which varies in accordance with the duration of operation under control of said first thermostat.

5. In a heating system, .a heating plant, an electrically controlled automatic stoker supplying fuel to said heating plant, and an electric circuit for the control of said stoker, said circuit including a first thermostat positioned in the space to be heated and an intermittent hold fire timer, said first thermostat being connected in such manner as to be capable of commencing the operation of said automatic stoker when said thermostat demands heat, regardless of said hold fire timer, said hold fire timer comprising contacts, connected in parallel with said iirst thermostat for controlling said stoker circuit, a plurality of heating devices, switching means for controlling said heatingdev'ices, a second thermostat having two phases, said second thermostat passing, at the attainment of a predetermined temperature during a heating phase, from its initial position to a second position, and, at the time of a predetermined lower temperature during a cooling phase, from its second position to its initial position, said second thermostat intermittently actuating said contacts and said switching means to provide intermittent operation of said stoker during periods of no heat demand and so controlling said heating devices as to provide first one rate of heating and then a different rate of heating during a cycle of operation, and means controlled by said flrst thermostat whereby operation of said stoker by said timer following a call for heat by said first thermostat is delayed for a period of time which varies in accordance with the duration of operation under control of said first thermostat.

6. In a heating system, a heating plant, an electrically controlled automatic stoker supplying fuel to said heating plant, and an electric circuit for the control of said stoker, said circuit including a first thermostat positioned in the space to be heated and an intermittent hold fire timer, said first thermostat being connected in such manner as to be capable of commencing the operation of said automatic stoker when said thermostat demands heat, regardless of said hold fire timer, said hold fire timer being inoperative for a limited period of time after operation of said stoker by said first thermostat to commence the operation of said stoker, said hold fire timer comprising contacts connected in parallel with said first thermostat for controlling said stoker circuit, a plurality of heating devices, switching means for controlling said heating devices, a second ther mostat for intermittently actuating said contacts and said switching means to provide intermittent operation of said stoker during periods of no heat demand and so controlling said heating devices as to provide first one rate of heating and then a diierent rate of heating during a cycle of operation, and means controlled by said first thermostat whereby operation ol said stoker by said timer following a call for heat by said first thermostat is delayed for a period of time which varies in accordance with the duration of operation under control of said iirst thermostat.

7. In a-heating system, a. heating plant, an electrically controlled automatic stoker supplying fuel to said heating plant, and an electric circuit for the control of said stoker, said circuit including a first thermostat positioned in the space to be heated and an intermittent hold fire timer, said rst thermostat being connected in such manner as to be capable of commencing the operation of said automatic stoker when said thermostat demands heat, regardless of said hold re timer, said hold fire timer comprising contacts connected in parallel with said first thermostat for controlling said stoker circuit, a plurality of heating devices, switching means for controlling said heating devices, a second thermostat having two phases, said second thermostat passing, at the attainment of a predetermined temperature during a heating phase, from its initial position to a second position, and, at the time of a predetermined lower temperature during a cooling phase, from its second position to its initial position, said second thermostat intermittently actuating said contacts and said switching means to provide intermittent operation of said stoker during periods of no heat demand and so controlling said heating devices as to provide first one rate of heating and then a different rate of heating during a cycle of operation, and means controlled by said first thermostat whereby operation of said stoker by said timer following a call for heat by said first thermostat is delayed for a period of time which varies in accordance with the duration of operation under control of said first thermostat, said second thermostat commencing a cooling phase immediately upon the cessation of operation of said stoker as caused by the first thermostat.

VICTOR G. VAUGHAN. JC HN D. BOLESKY. 

